Campaign spotlights little-known heart killer.
The British Cardiac Patients' Association says there is an urgent need to raise public awareness about unstable angina.
A survey conducted by the association showed that many people understood what normal angina was and that it causes chest pain.
But only 15 per cent of the 1,011 British adults questioned realised that unstable angina can lead to a heart attack, and just seven per cent knew it could be fatal.
Angina is a condition characterised by chest pain or tightness caused when the heart is not fed enough blood during periods of physical activity.
Although painful and frightening, it is not usually a medical emergency.
Unstable angina is far more serious. Although the symptoms are similar, it is unpredictable and often occurs when a person is at rest.
It results from a blood clot threatening the heart, and can rapidly lead to a heart attack and death.
Even if unstable angina is diagnosed and a hospital admission arranged, 2 per cent of patients will die before they are discharged and up to 15 per cent of victims will go on to have a heart attack.
A total of 1.4 million people in the UK suffer from angina, and each year there are nearly 120,000 hospital admissions for unstable angina.
Unstable angina can be recognised by symptoms of severe pain, nausea and sweating while a person is at rest.
The survey showed that people born in the Indian subcontinent, whose heart disease rates are 40 per cent higher than the population as a whole, were among the least aware of the seriousness of unstable angina.
The BCPA has set up a helpline to answer questions on heart disease and unstable angina which can be called on 020 8464 2417.